My 18 month old Havapeke, 12 lbs., has been vomiting for 24 hours. Last night she started yelping, crying and wriggling

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Obi is correct!!!
If any of my dogs EVER vomited for 24 hours they would have been at the vets after the first 5 or 6 hours!!!
Most likely at this point your dog is dehydrated, has a serious electrolyte imbalance and is in danger of dying if not treated immediately.
None of this even addresses WHY she is vomiting...most likely she has an obstruction which is extremely painful in itself.
Get off the internet and get her to your veterinarian immediately before it is too late!!!!